Self-teaching robot arm position method

ABSTRACT

A self-teaching robot arm positioning method that compensates for support structure component alignment offset entails the use of a component emulating fixture preferably having mounting features that are matable to support structure mounting elements. Robot arm mechanism motor angular position data measured relative to component emulating fixture features are substituted into stored mathematical expressions representing robot arm vector motion to provide robot arm position output information. This information indicates whether the actual relative alignment between the robot arm mechanism and a semiconductor wafer carrier is offset from a nominal relative alignment. For manual correction, robot arm mechanism position output information provides the angular offset between the actual and nominal radial distances between the robot arm mechanism shoulder axis and two locating features of the component emulating fixture. Position coordinates for proper alignment by manual repositioning of any misaligned wafer carrier can then be derived. For automatic correction, robot arm mechanism position output information is used to derive a vector trajectory that causes the end effector of the robot arm mechanism to properly access the wafer stored in a misaligned wafer carrier.

RELATED APPLICATIONS

This application is a continuation in part of U.S. patent applicationSer. No. 09/098,389, filed Jun. 16, 1998 now abandoned, which is adivision of U.S. patent application Ser. No. 08/500,489, filed Jul. 10,1995, now U.S. Pat. No. 5,765,444.

TECHNICAL FIELD

The present invention relates to robot arm mechanisms and, inparticular, to a self-teaching robot arm positioning method thatdetermines whether there exists misalignment of a specimen holderrelative to a robot arm mechanism to prevent the robot arm from reachingtoward an unintended location on the specimen holder.

BACKGROUND OF THE INVENTION

Currently available robot arm mechanisms include pivotally joinedmultiple links that are driven by a first motor and are mechanicallycoupled to effect straight line movement of an end effector or hand andare equipped with a second, independently operating motor to angularlydisplace the hand about a central axis. Certain robot arm mechanisms areequipped with telescoping mechanisms that move the hand also in adirection perpendicular to the plane of straight line movement andangular displacement of the hand. The hand is provided with a vacuumoutlet that secures a specimen, such as a semiconductor wafer, computerhard disk, or compact disk, to the hand as it transports the specimenbetween processing stations.

U.S. Pat. No. 4,897,015 of Abbe et al. describes a rotary-to-linearmotion robot arm that uses a first motor to control a multi-linkagerobot arm to produce straight line radial motion from motor-drivenrotary motion. An additional motor may be coupled to the robot arm foroperation independent of that of the first motor to angularly move themulti-linkage robot arm without radial motion. Because theyindependently produce radial motion and angular motion, the first andsecond motors produce useful robot arm movement when either one of themis operating.

The robot arm of the Abbe et al. patent extends and retracts an endeffector (or a hand) along a straight line path by means of a mechanismthat pivotally couples in a fixed relationship a first arm (or forearm)and a second (or upper) arm so that they move in predetermineddirections in response to rotation of the upper arm. To achieve angulardisplacement of the hand, a θ drive motor rotates the entire robot armstructure. The Abbe et al. patent describes no capability of the robotarm to reach around corners or travel along any path other than astraight line or a circular segment defined by a fixed radius.

U.S. Pat. No. 5,007,784 of Genov et al. describes a robot arm with anend effector structure that has two oppositely extending-hands, each ofwhich is capable of picking up and transporting a specimen. The endeffector structure has a central portion that is centrally pivotallymounted about the distal end of a second link or forearm. The extent ofpivotal movement about all pivot axes is purposefully limited to preventdamage to vacuum pressure flexible conduits resulting from kinking ortwisting caused by over-rotation in a single direction.

The coupling mechanism of a first link or upper arm, the forearm, andthe end effector structure of the robot arm of the Genov et al. patentis more complex than that of the robot arm of the Abbe et al. patent.Nevertheless, the robot arm structures of the Abbe et al. and Genov etal. patents operate similarly in that each of the end effectorstructures picks up and transports specimens by using one motor toextend and retract a hand and another, different motor to rotate theentire robot arm structure to allow the hand to extend and retract atdifferent ones of a restricted number of angular positions.

Robot arms of the type described by the Abbe et al. and Genov et al.patents secure a specimen to the hand by-means of vacuum pressuredelivered to the hand through fluid conduits extending through the upperarm, forearm, and hand and around all of the pivot axes. The Abbe et al.patent is silent about a vacuum pressure delivery system, and the Genovet al. patent describes the use of flexible fluid conduits. The presenceof flexible fluid conduits limits robot arm travel path planning becauseunidirectional robot arm link rotation about the pivot axes “winds up”the conduits and eventually causes them to break. Thus, conduit breakageprevention requirements prohibit-continuous robot arm rotation about anyof the pivot axes and necessitate rewind maneuvers and travel path“lockout” spaces as part of robot arm travel path planning. Theconsequences of such rewind maneuvers are more complex and limitedtravel path planning, reduced throughput resulting from rewind time, andreduced available work space because of the lockout spaces.

Moreover, subject to lockout space constraints, commercial embodimentsof such robot arms have delivered specimens to and retrieve specimensfrom stations angularly positioned about paths defined only by radialdistances from the axes of rotation of the robot arms.

Thus, the robot arm structures described by the Abbe et al. and Genov etal. patents are incapable of transporting specimens between processingstations positioned in compact, irregularly shaped working spaces. Forexample, neither of these robot arm structures is set up to removespecimen wafers from and place specimen wafers in wafer cassettes havingtheir openings positioned side-by-side in a straight line arrangement ofa tightly packed working space.

Wafer cassettes are usually positioned side by side on a supportstructure along a radial path measured from the central axis of or alonga straight line distance from the robot arm mechanism. These wafercassettes are often misaligned from their nominal cassette openingarrangements relative to the robot arm mechanism. Such misalignmentcould cause a robot arm mechanism to direct the hand or the wafer itcarries to strike the cassette instead of extend into its opening to,respectively, remove or replace a wafer. Robot arm mechanism contactwith the cassette resulting from alignment offset can, therefore, createcontaminant particles.

SUMMARY OF THE INVENTION

An object of the invention is, therefore, to provide a multiple linkrobot arm system that has straight line motion, extended reach, cornerreacharound, and continuous bidirectional rotation capabilities fortransporting specimens to virtually any location in an available workspace that is free of lockout spaces.

Another object of the invention is to provide such a system thatincreases specimen processing throughput in the absence of robot armrewind time and radial positioning of processing station requirements.

A further object of this invention is to provide such a system that iscapable of continuous rotation in either direction with nosusceptibility to kinking, twisting, or breaking of conduits deliveringvacuum pressure to the hand.

Still another object of the invention is to provide such a system thatuses two motors capable of synchronous operation and a linkage couplingmechanism that permit a hand of an end effector structure to change itsextension as the multiple link robot arm mechanism to which the hand isassociated changes its angular position.

Yet another object of the invention is to provide a system componentmisalignment correction technique for either mechanical alignment ofsystem it components or robot arm mechanism trajectory control tocompensate for support structure alignment offset.

Each of two preferred embodiments of the present invention includes twoend effectors or hands. A first embodiment comprises two multiple linkrobot arm mechanisms mounted on a torso link that is capable of 360degree rotation about a central or “torso” axis. Each robot armmechanism includes an end effector having a single hand. A secondembodiment is a modification of the first embodiment in that the formerhas one of the robot arm mechanisms removed from the torso link andsubstitutes on the remaining robot arm mechanism an end effector withoppositely extending hands for the end effector having a single hand.

Each of the multiple link robot arm mechanisms of the first and secondembodiments uses two motors capable of synchronized operation to permitmovement of the robot arm hand along a curvilinear path as the extensionof the hand changes. A first motor rotates a forearm about an elbow axisthat extends through distal and proximal ends of the upper arm andforearm, respectively, and a second motor rotates an upper arm about ashoulder axis that extends through a proximal end of the upper arm. Amechanical linkage couples the upper arm and the forearm. The mechanicallinkage forms an active drive link and a passive drive link. The activedrive link operatively connects the first motor and the forearm to causethe forearm to rotate about the elbow axis in response to the firstmotor. The passive drive link operatively connects the forearm and thehand to cause the hand to rotate about a wrist axis in response torotation of the forearm about the elbow axis. The wrist axis extendsthrough distal and proximal ends of the forearm and hand, respectively.

In two embodiments described in detail below, a motor controllercontrols the first and second motors in two preferred operational statesto enable the robot arm mechanism to perform two principal motionsequences. The first operational state maintains the position of thefirst motor and rotates the second motor so that the mechanical linkagecauses linear displacement (i.e., extension or retraction) of the hand.The second operational state rotates the first and second motors so thatthe mechanical linkage causes angular displacement of the hand about theshoulder axis. The second operational state can provide an indefinitenumber of travel paths for the hand, depending on coordination of thecontrol of the first and second motors.

Whenever the first and second motors move equal angular distances, theangular displacement of the upper arm about the shoulder axis and theangular displacement of the forearm about the elbow axis equally offsetand thereby result in only a net angular displacement of the hand aboutthe shoulder axis. Thus, under these conditions, there is no lineardisplacement of the hand and no rotation of the hand about the wristaxis. Whenever the first and second motors move different angulardistances, the angular displacement of the upper arm about the shoulderaxis and the angular displacement of the forearm about the elbow axisonly partly offset and thereby result in angular displacements of thehand about the shoulder and wrist axes and consequently a linear isdisplacement of the hand. Coordination of the position control of thefirst and second motors enables the robot arm mechanism to describe acompound curvilinear path of travel for the hand.

A third or torso motor rotates the torso link about the central axis,which extends through the center of the torso link and is equidistantfrom the shoulder axes of the robot arm mechanisms of the firstembodiment. The motor controller controls the operation of the torsomotor to permit rotation of the torso link independent of the motion ofthe robot arm mechanism or mechanisms mounted to it. The presence of therotatable torso link together with the independent robot arm motionpermits simple, nonradial positioning of specimen processing stationsrelative to the torso axis, extended paddle reach, and cornerreacharound capabilities. The consequence is a high speed, highthroughput robot arm system that operates in a compact work space.

Each of the robot arm mechanisms of the first embodiment is equippedwith a rotary fluid slip ring acting as a fluid feedthrough conduit.These slip rings permit the hand to rotate continuously in a singledirection as the robot arm links rotate continuously about the shoulder,elbow, and wrist axes without a need to unwind to prevent kinking ortwisting of fluid pressure lines. Vacuum pressure is typically deliveredthrough the fluid pressure lines.

The robot arm mechanism of the second embodiment is equipped with arotary fluid multiple-passageway spool that delivers fluid pressureseparately to each rotary joint of and permits continuous rotation ofthe robot arm links in a single direction about the central, shoulder,elbow, and wrist axes.

Preferred embodiments implementing the self-teaching robot armpositioning method to compensate for support structure alignment offsetneed not include two end effectors or hands. A misalignment correctiontechnique carried out in accordance with the invention entails the useof a component emulating fixture preferably having mounting featuresthat are matable to support structure mounting elements. The emulatingfixture preferably includes two upwardly extending, cylindrical locatingfeatures that are positioned to engage a fork-shaped end effector in twodifferent extension positions. The robot arm positioning method is selfteaching in that the motor angular position data measured relative tothe fixture features are substituted into stored mathematicalexpressions representing robot arm mechanism motion to provide robot armposition output information that determines the alignment position ofthe wafer carrier and thereby the existence of error in its actualalignment relative to a nominal alignment.

For manual correction, robot arm mechanism position output informationprovides the angular offset between the actual and nominal radialdistances between the robot arm mechanism shoulder axis and the twolocating features. Position coordinates for proper alignment by manualrepositioning of any misaligned wafer carrier can then be derived. Forautomatic correction, robot arm mechanism position output information isused to derive a trajectory that causes the end effector to properlyaccess the wafers stored in a misaligned wafer carrier.

Additional objects and advantages of this invention will be apparentfrom the following detailed description of preferred embodiments thereofwhich proceeds with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A, 1B, and 1C are respective side elevation, plan, andcross-sectional views of a two-arm, multiple link robot arm system ofthe present invention.

FIG. 2 is a side elevation view in stick diagram form showing the linkcomponents and the associated mechanical linkage of the robot arm systemof FIGS. 1A, 1B, and 1C.

FIG. 3 is an isometric view in stick diagram form showing the rotationalmotion imparted by the motor drive links of the mechanical linkage ofthe robot arm system of FIGS. 1A, 1B, and 1C.

FIGS. 4A and 4B are respective cross-sectional and fragmentary planviews showing the interior components, mechanical linkage, and fluidpressure line paths of the robot arm system of FIGS. 1A, 1B, and 1C.

FIGS. 5A and 5B are respective side elevation and plan views of a rotaryfluid slip ring installed at each rotary joint of the robot arm systemof FIGS. 1A, 1B, and 1C.

FIG. 6A is a diagram showing the spatial relationships and parametersthat are used to derive control signals provided by, and FIG. 6B is ablock diagram of, the motor controller for the embodiments of the dualend effector, multiple link robot arm system of the invention.

FIGS. 7A and 7B are respective side elevation and plan views of analternative one-arm, multiple link robot arm system having an endeffector structure with two oppositely extending hands.

FIGS. 8A-1 and 8A-2 and FIG. 8B are respective fragmentarycross-sectional and plan views showing the interior components,mechanical linkage, and fluid pressure line paths of the robot armsystem of FIGS. 7A and 7B.

FIGS. 9A and 9B are respective side elevation and plan views of therotary multiple fluid-passageway spool installed in each rotary joint ofthe robot arm system of FIGS. 8A and 8B.

FIG. 10 shows in a series of 16 frames the various positions of thetwo-arm, multiple link robot arm system of FIGS. 1A, 1B, and 1C as itretrieves two specimens from two parallel-aligned storage locations andsequentially places the two specimens temporarily at a process location.

FIG. 11 shows in a series of 19 frames the various positions of aone-arm, two-hand multiple link robot arm system of FIGS. 7A and 7B asit retrieves two specimens from parallel-aligned storage locations andsequentially places the two specimens temporarily at a process location.

FIG. 12 shows an upper surface of a support structure adapted to receivea front-opening wafer carrier for 300 mm diameter semiconductor wafers.

FIG. 13A shows a wafer carrier with its carrier or box door removed toreveal the interior of the wafer carrier; and FIGS. 13B and 13C show,respectively, a bottom surface and a carrier front retaining feature onthe bottom surface of the wafer carrier.

FIGS. 14A and 14B are respective bottom and top plan views of acomponent emulating fixture of the invention.

FIGS. 15A and 15B are respective diagrammatic cross-sectional and rearend elevation views of the component emulating fixture of FIGS. 14A and14B.

FIGS. 16A, 16B, and 16C are, respectively, a bottom plan view of thecomponent emulating fixture superimposed on an outline of the wafercarrier, a side elevation view of the fixture similar to that of FIG.15A, and a rear end view of the fixture inverted relative to that ofFIG. 15B.

FIG. 17 shows two wafer carriers positioned side by side with theirfront openings in a nominal coplanar relation, similar to that depictedin FIG. 6A.

FIG. 18 shows two wafer carriers positioned side by side but with one ofthem offset such that their front openings are misaligned from thenominal coplanar position shown in FIG. 17.

FIG. 19 is a diagram showing two radii representing distances between arobot arm mechanism shoulder axis and locating feature longitudinal axisfor the extension of the end effector to two locating features of thecomponent emulating fixture.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIGS. 1A, 1B, and 1C are respective side elevation, plan, andcross-sectional views of a two-arm, multiple link robot arm system 8mounted on and through an aperture in the top surface of a support table9.

With reference to FIGS. 1A and 1B, two similar but independentlycontrollable three-link robot arm mechanisms 10L and 10R are rotatablymounted at opposite ends of a torso link 11, which is mounted to the topsurface of a base housing 12 for rotation about a central or torso axis13. Because they are mirror images of each other, robot arm mechanisms10L and 10R have corresponding components identified by identicalreference numerals followed by the respective suffices “L” and “R”.Accordingly, the following discussion is directed to the constructionand operation of only robot arm mechanism 10R but is similarlyapplicable to robot arm mechanism 10L.

Robot arm mechanism 10R comprises an upper arm 14R mounted to the topsurface of a cylindrical spacer 15R, which is positioned on theright-hand end of torso link 11 for rotation about a shoulder axis 16R.Cylindrical spacer 15R provides room for the motors and certain othercomponents of robot arm mechanism 10R, as will be described below. Upperarm 14R has a distal end 18R to which a proximal end 20R of a forearm22R is mounted for rotation about an elbow axis 24R, and forearm 22R hasa distal end 26R to which a proximal end 28R of a hand 30R is mountedfor rotation about a wrist axis 32R. Hand 30R is equipped at its distalend 34R with a fluid pressure outlet 36R that preferably applies vacuumpressure supplied to robot arm mechanism 10R at an inlet 38 to securelyhold a semiconductor wafer, compact disk, or other suitable specimen(not shown) in place on hand 30R. As will be described in detail later,each of upper arm 14R, forearm 22R, and hand 30R is capable ofcontinuous rotation about its respective shoulder axis 16R, elbow axis24R, and wrist axis 32R.

FIG. 2 shows the link components and associated mechanical linkage ofrobot arm mechanism 10R. With reference to FIG. 2, robot arm mechanism10R is positioned by first and second concentric motors 50R and 52R thatoperate in response to commands provided by a motor controller 54 (FIGS.6A and 6B). First motor 50R rotates forearm 22R about elbow axis 24R,and second motor 52R rotates upper arm 14R about shoulder axis 16R.

More specifically, first motor 50R rotates a forearm spindle 56R thatextends through an aperture in upper arm 14R and terminates in an upperarm pulley 58R. A post 60R extends upwardly at distal end 18R of upperarm 14R through the center of a bearing 62R that is mounted to a bottomsurface 64R of forearm 22R at its proximal end 20R. Post 60R alsoextends through an aperture in forearm 22R and terminates in a forearmpulley 66R. An endless belt 68R connects upper arm pulley 58R and theouter surface of bearing 62R to rotate forearm 22R about elbow axis 24Rin response to rotation of first motor 50R.

Second motor 52R rotates an upper arm spindle 80R that is mounted to abottom surface 82R of upper arm 14R to rotate upper arm 14R aboutshoulder axis 16R. Coordinated operation of first and second motors 50Rand 52R in conjunction with the mechanical linkage described belowcauses hand 3OR to rotate about shoulder axis 16R. A post 84R extendsupwardly through the center of a bearing 86R that is mounted to a bottomsurface 88R of hand 30R. An endless belt 90R connects forearm pulley 66Rto the outer surface of bearing 86R to rotate hand 30R about shoulderaxis 16R in response to the coordinated rotational motions of motors 50Rand 52R.

The mechanical linkage coupling upper arm 14R and forearm 22R forms anactive drive link and a passive drive link. The active drive linkincludes belt 68R connecting upper arm pulley 58R and the outer surfaceof bearing 62R and causes forearm 22R to rotate in response to rotationof first motor 50R. The passive drive link includes belt 90R connectingforearm pulley 66R and the outer surface of bearing 86R and causes hand30R to rotate about wrist axis 32R in response to rotation of forearm22R about elbow axis 24R. Rotation of hand 30R can also be caused by acomplex interaction among the active and passive drive links and therotation of upper arm 14R in response to rotation of second motor 52R.

A third or torso motor 92 rotates a torso link spindle 94 that ismounted to a bottom surface of torso link 11, to which robot armmechanism 10R is rotatably mounted. A main ring 96 supports a bearingassembly 98 around which spindle 94 rotates. Motor 92 is capable of 360degree continuous rotation about central axis 13 and therefore can, incooperation with robot arm mechanism 10R, move hand 30R along anirregular path to any location within the reach of hand 30R.

Motor controller 54 (FIGS. 6A and 6B) controls motors 50R and 52R in twopreferred operational states to enable robot arm mechanism 10R toperform two principal motion sequences. The first motion sequencechanges the extension or radial position of hand 30R, and the secondmotion sequence changes the angular position of hand 30R relative toshoulder axis 16R. FIG. 3 is a useful diagram for showing the two motionsequences.

With reference to FIGS. 2 and 3, in the first operational state, motorcontroller 54 causes first motor 50R to maintain the position of forearmspindle 56R and second motor 52R to rotate upper arm spindle 80R. Thenon-rotation of first motor 50R maintains the position of upper armpulley 58R, and the rotation of upper arm spindle 80R by second motor52R rotates upper arm 14R about shoulder axis 16R, thereby causingrotation of forearm 22R about elbow axis 24R and counter-rotation ofhand 30R about wrist axis 32R. Because the ratio of the diameters ofupper arm pulley 58R and the outer surface of bearing 62R are 4:2 andthe ratio of the diameters of forearm pulley 66R and the outer surfaceof bearing 86R is 1:2, the rotation of upper arm 14R in a directionspecified by P₂ shown in FIG. 3 will cause hand 30R to move along astraight line path 100. (The diameters of forearm pulley 66R and theouter surface of bearing 86R are one-half of the diameters of,respectively, the outer surface of bearing 62R and upper arm pulley 58Rto streamline the sizes and shapes of forearm 22R and hand 30R.)

Whenever upper arm 14R rotates in the clockwise direction specified byP₂, hand 30R extends (i.e., increases radial distance from shoulder axis16R) along path 100. Whenever upper arm 14R rotates in thecounter-clockwise direction specified by P₂, hand 30R retracts (i.e.,decreases radial distance from shoulder axis 16R) along path 100.Skilled persons will appreciate that robot arm mechanism 10 in a mirrorimage configuration of that shown in FIG. 3 would extend and retract inresponse to upper arm 14 rotation in directions opposite to thosedescribed. FIG. 1B shows that when robot arm mechanism 10R is extended,axes 13, 16R, 24R, and 32R are collinear.

In the second operational state, motor controller 52R causes first motor50R to rotate forearm spindle 56R in the direction specified by P₁ andsecond motor 52R to rotate upper arm spindle 80R in the directionspecified by P₂. In the special case in which motors 50R and 52R aresynchronized to rotate in the same directions by the same amount ofdisplacement, hand 30R is only angularly displaced about shoulder axis16R. This is so because the rotation of forearm 22R about elbow axis 24Rcaused by the rotation of first motor 50R and the rotation of hand 30Rabout wrist axis 32R caused by rotation of second motor 52R and theoperation of the passive drive link offset each other to produce no netrotation about elbow axis 24R and wrist axis 32R. Thus, hand 30R isfixed radially at a point along path 100 and describes a circular pathas only upper arm 14R rotates about shoulder axis 16R. By application ofkinematic constraints to achieve a desired travel path for hand 30,motor controller 54 can operate first and second motors 50R and 52R tomove robot arm mechanism 10R along non-radial straight line paths, aswill be further described below.

Skilled persons will appreciate that to operate robot arm mechanism 10R,first and second motors 50R and 52R are coupled by either rotating bothof them or grounding one while rotating the other one. For example,robot arm mechanism 10R can be operated such that forearm 22R rotatesabout elbow axis 24R. Such motion would cause hand 30R to describe asimple spiral path between shoulder axis 16R and the full extension ofhand 30R. This motion is accomplished by fixing the position of shoulder14R and operating motor 50R to move forearm 22R. Applicants note thatthe prior art described above is incapable of rotating the elbow jointwithout also rotating the shoulder joint, thereby requiring theoperation of two motors.

Motor controller 54 controls the operation of torso motor 92 andtherefore the rotation of torso link 11 in a direction specified by P₃independently of the operational states of motors 50R and 52R.

FIGS. 4A and 4B show the interior components, mechanical linkage, andfluid pressure conduits of robot arm mechanism 10R shown in FIGS. 1A,1B, and 1C. With reference to FIGS. 4A and 4B, a motor housing composedof an interior portion of torso link 11 and a cylindrical spacer 15Rcontains first motor 50R and second motor 52R arranged in concentricrelation such that their respective forearm spindle 56R and upper armspindle 80R rotate about shoulder axis 16R. Forearm spindle 56R ispositioned nearer to shoulder axis 16R and is directly connected toupper arm pulley 58R journalled for rotation on bearings 102R. Upper armspindle 80R is positioned farther radially from shoulder axis 16R and isdirectly connected to bottom surface 82R of upper arm 14R journalled forrotation on bearings 104R. The angular positions of motors 50R and 52Rare tracked by respective glass scale encoders 106R and 108R. Encoders106R and 108R include respective annular diffraction grating scales 110Rand 112R and respective light source/detector subassemblies (not shown).Such glass scale encoders are known to skilled persons.

Base housing 12 contains motor 92, which is arranged such that torsolink spindle 94 journalled on bearings 98 rotates about central axis 13.The angular position of motor 92 is tracked by a glass scale encoder 118of a type similar to encoders 106R and 108R.

Robot arm system 8 includes two separate fluid pressure conduits 124Land 124R each including multiple path segments, with conduit 124Lextending between fluid pressure inlet 38L and outlet 36L of fluidpocket or land 126L and conduit 124R extending between fluid pressureinlet 38R and outlet 36R of land 126R. In the preferred embodimentsdescribed, the fluid pressure conduits deliver vacuum pressure but arecapable of delivering positive amounts of fluid pressure. Each of pathsegments 128L and 128R in base housing 12 and of path segments 129L and129R in torso link 11 is partly a flexible hose and partly a hole in asolid component.

Path segments 130R, 132R, and 134R in the respective upper arm 14R,forearm 22R, and hand 30R are either channels formed by complementarydepressions in mating components or holes passing through solidcomponents. Outlet 36R constitutes a hole in vacuum land 126R on thespecimen-contacting surface of hand 30R.

Each path segment terminating or originating at shoulder axis 16R, elbowaxis 24R, and wrist axis 32R includes a rotary fluid slip ring 136 thatfunctions as a vacuum feedthrough conduit that permits continuousrotation about any one of these three axes. Path segments 128R and 129Rare joined at central axis 13 by an enlarged version of a rotarymultiple fluid-passageway spool 300, which rotates within a bearingassembly 120 supported by main ring 96. Spool 300 is described belowwith reference to FIGS. 9A and 9B in connection with the detaileddescription of the alternative preferred embodiment.

FIGS. 5A and 5B show rotary fluid slip ring 136, which is fitted intoeach of the rotary joints at shoulder axis 16R, elbow axis 24R, andwrist axis 32R. For purposes of convenience only, the followingdescribes the operation of slip ring 136 in the rotary joint definingwrist axis 32R.

With reference to FIGS. 4A, 4B, 5A, and 5B, slip ring 136 includes aconvex upper surface 142 and a convex lower surface 144 separated by anannular leaf spring 146. Each of surfaces 142 and 144 is preferably madeof a reinforced Teflon® co-polymer and has a central aperture 148. Whenit is fitted in a rotary joint, slip ring 136 receives through centralaperture 148 a protrusion 150 from the top surface of post 84R thatextends from distal end 26R of forearm 22R. Protrusion 150 has a hole152 that extends into and through post 84R along its entire length andis in fluid communication with vacuum path segment 132R within forearm22R. The wrist joint formed by forearm 22R and hand 30R causes uppersurface 142 to fit against an interior vacuum channel surface 154R ofhand 30R and lower surface 144 to fit against a depression 156R in thetop surface of post 84R. The raised upper and lower surfaces 142 and 144compress against leaf spring 146 and form a vacuum seal for the spacebetween the top of protrusion 150 and vacuum channel surface 154R ofhand 30R. The reinforced co-polymer material from which upper surface142 is made forms a bearing surface that maintains a vacuum-tight sealduring rotary motion about wrist axis 32R.

The mechanical construction of robot arm mechanism 10 does not restricthand 30R to straight line motion but provides two degrees of freedom toachieve complex trajectories. This is beneficial because it facilitatesspecimen processing layouts to provide relatively small footprints andprocessing component placements that enhance ergonomic loading ofspecimens. A common application is to access specimens in straight linerather than complex hand movements. Thus, the following descriptiongives an example of how a skilled person would implement controller 54to carry out this common specimen access operation.

FIG. 6A is a diagram that specifies a local coordinate axis frame whoseaxes are defined by the orientation of a semiconductor wafer cassette168 _(r) and its location relative to shoulder axis 16R. With referenceto FIG. 6A, the following description sets forth the mathematicalexpressions from which are derived the command signals controller 54uses to retrieve from cassette 168 _(r) a wafer 170 _(r) along a vectorperpendicular to the opening of cassette 168 _(r).

The following parameters are pertinent to the derivation of the path oftravel of hand 30:

θ_(S)=angle of motor 52R

θ_(E)=angle of motor 50R

r=distance between shoulder axis 16R and elbow axis 24R and distancebetween elbow axis 24R and wrist axis 32R

β=angle between upper arm 14R and forearm 22R

p=length of hand 30R

E=2r=extension of robot arm

R_(i)=reach of robot arm (i.e., its radius measured from shoulder axis16R to the center 172 _(r) of wafer 170 _(r) positioned on hand 30R).

Application of the law of cosines provides the following expressions forR_(i): $\begin{matrix}\begin{matrix}{R_{i} = {p + \sqrt{\left( {r^{2} + r^{2} - {2r^{2}\cos \quad \beta}} \right)}}} \\{= {p + {\sqrt{2}r{\sqrt{\left( {1 - {\cos \quad \beta}} \right)}.}}}}\end{matrix} & (1)\end{matrix}$

For β=0, equation (1) provides that R_(i)=p and x=0, y=0, Θ_(S)=Θ_(S)_(r) , Θ_(E)=Θ_(E) _(R) . The quantities Θ_(S) _(R) and Θ_(E) _(R)represent reference motor angles. The motor angles may be expressed asΘ_(S)=ΘS _(R) +ΔΘ_(S) _(R) , Θ_(E)=|73 _(E) _(R) +ΔΘ_(E) _(R) . Theangle β may be expressed as β=2(ΔΘ_(S) _(R) −ΔΘ_(E) _(R) ) because ofthe construction of the mechanical linkages of robot arm mechanism 10R.This equation relates the angle β to changes in the motor angles.

To retrieve wafer 170 _(r) from cassette 168 _(r) along a straight linepath, the displacement along the X-axis equals X₀, which is a constant.Thus, X(t)=X0. The quantity X(t) can be expressed as a function of thelengths of the X-axis components of its links:

X(t)=r cos Θ₁+r cos Θ₂+p cos Θp,  (2)

in which

θ₁=angle of upper arm 14R

θ₂=angle of forearm 22R

θ_(p)=angle of hand 30R.

Because upper arm 14R and forearm 22R are of the same length (r), θ₁tracks the angle θ_(S) of motor 52R, and hand 30R moves in a straightline, the following expressions hold: Θ₁ = Θ_(S) Θ₂ = Θ₁ + π − β$\Theta_{p} = {\Theta_{i} + {\left( \frac{\pi - \beta}{2} \right).}}$

Thus, to compute X₀, one substitutes the foregoing identities for θ₁,θ₂, and θ_(p) into equation (2) for X(t) and finds: $\begin{matrix}\begin{matrix}{X_{0} = {{r\left( {{\cos \quad \Theta_{1}} + {\cos \quad \Theta_{2}}} \right)} + {p\quad \cos \quad \Theta_{p}}}} \\{X_{0} = {{r\left( {{\cos \quad \Theta_{1}} + {\cos \quad \left( {\Theta_{1} + \pi - \beta} \right)}} \right)} + {p\quad \cos \quad \left( {\Theta_{1} + \frac{\pi}{2} - \frac{\beta}{2}} \right)}}} \\{X_{0} = {{r\left( {{\cos \quad \Theta_{1}} - {\cos \quad \left( {\Theta_{1} - \beta} \right)}} \right)} - {p\quad {{\sin \left( {\Theta_{1} - \frac{\beta}{2}} \right)}.}}}}\end{matrix} & (3)\end{matrix}$

Equation (3) expresses the constraint that sets but the relationshipbetween the angles θ_(S) and θ_(E) of motors 52R and 50R operating tomove equal angular distances to achieve straight line movement of hand30R.

Skilled persons can implement constraint equation (3) by means of aservomechanism controller in any one of a number of ways. For example,to achieve high speed operation to implement a given wafer move profileone can compute from equation (3) command signal values and store themin a look-up table for real-time use. The precomputation process wouldentail the indexing of θ_(S) in accordance with the wafer move profileand determining from equation (3) the corresponding θ_(E) values,thereby configuring the displacement of θ_(S) and θ_(E) in amaster-slave relationship.

To achieve angular displacement of hand 30R about shoulder axis 16R,controller 54 causes motors 50R and 52R to rotate in the same directionthrough the desired angular displacement of hand 30R to reach thedesired destination. The linear extension of hand 30R does not changeduring this move. Skilled persons will appreciate that complicatedconcurrent linear and angular displacement move profiles of hand 30Rcould be accomplished by programming controller 54 to operate motors 50Rand 52R through different angular displacements. FIG. 6A shows a secondwafer cassette 168 _(l) positioned so that the center 172 _(l) of astored wafer 170 _(l) is coincident to Y₀. The parallel arrangement ofthe openings of cassettes 168 _(l) and 168 _(r) demonstrates that theabove expressions can be used to retrieve wafers stored in cassettes notpositioned a radial distance from shoulder axis 16. Such nonradialplacement is not implemented in the prior art references describedabove. Robot arm mechanism 10 is not restricted to radial placement butcan accommodate any combination of distances within its reach.

FIG. 6B is a simplified block diagram showing the primary components ofcontroller 54. With reference it to FIG. 6B, controller 54 includes aprogram memory 174 that stores move sequence instructions for robot armmechanism 10R. A microprocessor 176 receives from program memory 174 themove sequence instructions and interprets them to determine whether thefirst or second operational state is required or whether motion of motor92 is required to position torso link 11. A system clock 178 controlsthe operation of microprocessor 176. A look-up table (LUT) 180 storescorresponding values for θ_(S) (motor 52R) and θ_(E) (motor 50R) toaccomplish the straight line motion of the first operational state andthe angular displacements of θ_(S) and θ_(E) to accomplish the angularmotion of the second operational state. Because the rotation of torsolink 11 is independent of the motions of the robot arm mechanismsmounted to it, the overall coordination of the angular displacement ofmotor 92 with the angular displacements of motors 50R and 52R is carriedout in the move sequence instructions, not in LUT 180. This results inhigher speed and more accurate straight line motion because multipleaxis servomechanism following errors and drive accuracy errors do notaffect the straight line path of hand 30R.

Microprocessor 176 provides θ_(S)and θ_(E) position signals to aservomechanism amplifier 182, which delivers θ_(S) and θ_(E) commandsignals to motors 52R and 50R, respectively. Microprocessor 176 alsoprovides position signals to servomechanism amplifier 176 to deliver acommand signal to torso motor 92. Servomechanism amplifier 182 receivesfrom glass scale encoders 106, 108, and 118 signals indicative of theangular positions of the respective motors 50R, 52R, and 92.

Microprocessor 176 also provides control signals to a vacuum valvecontroller 184, which causes a vacuum valve (not shown) to provide froma vacuum source (not shown) an appropriate amount of vacuum pressure tooutlet 36 in response to the need to hold a wafer on or release a waferfrom hand 30R.

FIGS. 7A and 7B show an alternative one-arm, multiple link robot armsystem 208 of similar design to robot arm system 8 with the significantexceptions that robot arm mechanism 10L is absent and the consequentexcess length of torso link 11 is removed, and an end effector structure230 having two oppositely extending hands 30, and 302 is substituted forhand 30R. FIGS. 8A and 8B show the interior components, mechanicallinkage, and vacuum pressure line paths of robot arm mechanism 208.Because of the similarity of robot arm systems 8 and 208, theircorresponding components and axes of rotation are identified byidentical reference numerals. For purposes of clarity, the suffix “R”has been omitted.

With reference to FIGS. 7A and 7B, end effector structure 230 includesoppositely extending hands 30, and 30 ₂ that rotate about wrist axis 32.Because they retrieve and deliver separate specimens, hand 30 ₁ has avacuum land 126 ₁ with an outlet 36 ₂ and hand 30 ₂ has a vacuum land126 ₂ with an outlet 36 ₂ that are connected to separate vacuum pressureconduits routed within base housing 12, torso link 11, upper arm 14, andforearm 22.

With reference to FIGS. 8A-1 and 8A-2 (collectively, “FIG. 8A”) and FIG.8B, robot arm mechanism 210 includes two separate vacuum pressureconduits 124 ₁ and 124 ₂ each including multiple path segments, withconduit 124 ₁ extending between vacuum pressure inlet 38 ₁ and outlet 36₁ of vacuum land 126 ₁ and conduit 124 ₂ extending between vacuumpressure inlet 38 ₂ and outlet 36 ₂ of vacuum land 126 ₂. Path segments128 ₁ and 128 ₂ of the respective conduits 124 ₁ and 124 ₂ are flexiblehoses. Path segments 129 ₁ and 129 ₂ in torso link 11, path segments 130₁ and 130 ₂ in upper arm 14, path segments 132 ₁ and 132 ₂ in forearm22, and path segments 134 ₁ and 134 ₂ in the respective hands 30 ₁ and30 ₂ are either channels formed by complementary depressions in matingcomponents or holes passing through solid components.

Outlets 36 ₁ and 36 ₂ constitute holes in the respective vacuum lands126 ₁ and 126 ₂. Each path segment of conduits 124 ₁ and 124 ₂terminating or originating at central axis 13, shoulder axis 16, elbowaxis 24, and wrist axis 32 includes a rotary multiple fluid-passagewayspool 300 that functions as two independent vacuum feedthrough conduitsthat permit continuous rotation about any one of these four axes. Theplacement of spool 300 fitted in each of the three rotary joints ofrobot arm mechanism 210 is shown in FIGS. 8A and 8B. FIGS. 9A and 9Bshow the design detail of a prior art rotary multiple fluid-passagewayspool 300.

With reference to FIGS. 8A, 8B, 9A, and 9B, spool 300 comprises a solidmetal cylindrical body 302 having two spaced-apart grooves 304 and 306formed in and encircling its outer side surface 308 about a longitudinalaxis 310. Two separate vacuum pressure delivery channels 312 and 314 areformed within and pass through body 302. (Comparison of FIGS. 8A and 8Bwith FIG. 9B reveals that vacuum pressure delivery channels 312 and 314formed within body 302 by artistic license are drawn rotated by 90degrees in FIG. 8A only to show clearly the vacuum pressure conduits.)Each of channels 312 and 314 has two passageway segments, oneoriginating in a groove and the other terminating at a top surface 316of body 302. More specifically, for channel 312, a passageway segment318 extends inwardly from groove 304 in a direction transverse tolongitudinal axis 310 and intersects with a passageway segment 320 at aright angle juncture. Passageway segment 320 extends upwardly toward andthrough top surface 316 in a direction parallel to longitudinal axis310. Similarly, for channel 314, a passageway segment 322 extendsinwardly from groove 306 in a direction transverse to longitudinal axis310 and intersects with a passageway segment 324 at a right anglejuncture. Passageway segment 324 extends upwardly toward and through topsurface 316 in a direction parallel to longitudinal axis 310.

For purposes of convenience only, the following describes the operationof spool 300 in the rotary joint defining wrist 32. When spool 300 isfitted into forearm 22, four seal rings 330 spaced above, between (twoseals), and below grooves 304 and 306 form two annular gas spaces 332and 334 between side surface 308 of spool 300 and an interior surface336 of forearm 22. Spacers 338 that extend about 330 degrees aroundspool 300 in grooves 304 and 306 maintain the desired separation betweenadjacent seal rings 330. Vacuum path segments 134 ₁ and 134 ₂ terminatein the respective gas spaces 332 and 334 and their corresponding holesin top surface 316 of spool 300, thereby coupling the vacuum pressuresupply to and from spool 300.

FIG. 10 includes 16 frames showing various positions of robot armmechanisms 10L and 10R of robot arm system 8 in an exemplary operationalsequence that moves a wafer A from a left-side wafer cassette 352L to aprocessing station 350 (such as a cooling platform) and back to leftwafer cassette 352L, moves a wafer P from left wafer cassette 352L toprocessing station 350, and retrieves a wafer C from a right-side wafercassette 352R.

In this example, in the initial position shown in frame 1, left shoulderaxis 16L is radially positioned 40.0 centimeters (15.8 inches) from aneffective center. 351 of processing station 350 and an effective center353L of cassette 352L. Right shoulder axis 16R is radially positioned40.0 centimeters (15.8 inches) from center 351 of processing station 350and an effective center 353R of cassette 352R. Axes 16L and 16R andcenters 353L and 353R define four corners of a rectangle with axes 16Land 16R being spaced apart a distance of 35.5 centimeters (14.0 inches)and cassettes 352L and 352R being spaced apart a distance of 35.5centimeters (14.0 inches) from center to center. Cassettes 352L and 352Rare spaced apart from respective axes 16R and 16L a non-radial distanceof 53.5 centimeters (21.1 inches) measured along the respectivediagonals of the rectangle. Torso movement rotation of shoulders 14L and14R, as shown in frame 14, radially positions axes 16L and 16R adistance of 40.0 centimeters (15.8 inches) from effective centers 353Rand 353L.

The following description tracks the angular displacement of torso link11 about central axis 13, upper arm 14R about shoulder axis 16R, andupper arm 14L about shoulder axis 16L to demonstrate the continuousrotation capabilities of torso link 11 and the mechanical links in robotarm mechanisms 10R and 10L.

Frame 1 shows the initial positions of hands 30L and 30R retracted andin line with the openings of the respective cassettes 352L and 352R. Inthese initial positions, the central longitudinal axis of upper arm 14L(i.e., a line connecting axes 16L and 24L) is angularly displaced 67.5degrees in a counter-clockwise direction from a reference line 354, andthe central longitudinal axis of upper arm 14R (i.e., a line connectingaxes 16R and 24R) is angularly displaced 67.5 degrees in a clockwisedirection from reference line 354. Reference line 354 is perpendicularto a line connecting centers 353L and 353R.

Frame 2 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of motor controller 54 to linearly extendhand 30L so as to reach and retrieve wafer A from cassette 352L. Toaccomplish this incremental movement, upper arm 14L rotated 112.5degrees in a counter-clockwise direction about shoulder axis 16L.

Frame 3 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of motor controller 54 to linearly retracthand 30L holding wafer A after the application of vacuum pressure atoutlet 36L to secure wafer A to hand 30L. To accomplish this incrementalmovement, upper arm 14L rotated 112.5 degrees in a counter-clockwisedirection about shoulder axis 16L.

Frame 4 shows upper arm 14L rotating 153.65 degrees in acounter-clockwise direction along a circular path segment 355 aboutshoulder axis 16L in the second operational state of motor controller 54to keep hand 30L retracted while holding wafer A, hold forearm 22Lstationary, and position hand 30L in line with processing station 350.Upon completion of this incremental movement, upper arm 14L exceeded acontinuous 360 degree cycle of counter-clockwise rotation.

Frame 5 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of controller 54 to linearly extend hand 30Lso as to reach and place wafer A on processing station 350. Toaccomplish this incremental movement, upper arm 14L rotated 112.5degrees in a clockwise direction about shoulder axis 16L.

Frame 6 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of controller 54 to linearly retract hand30L after the release of vacuum pressure at outlet 36L to leave wafer Aat processing station 350. To accomplish this incremental movement,upper arm 14L rotated 112.5 degrees in a counter-clockwise directionabout shoulder axis 16L.

Frame 7 shows upper arm 14L rotating 153.65 degrees in a clockwisedirection along a circular path segment 356 about shoulder axis 16L inthe second operational state of controller 54 to keep hand 30Lretracted, hold forearm 22L stationary, and position hand 30L in linewith cassette 352L.

Frame 8 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of controller 54 to linearly extend hand 30Lto retrieve wafer B from cassette 352L. To accomplish this incrementalmovement, upper arm 14L rotated 112.5 degrees in a clockwisedirection:.about shoulder axis 16L.

Frame 9 shows simultaneous rotation of upper arms 14L and 14R. Upper arm14L and forearm 22L cooperatively rotate in the first operational stateof controller 54 to linearly retract hand 30L holding wafer B after theapplication of vacuum pressure at outlet 36L to secure wafer B to hand30L. To accomplish this incremental movement, upper arm 14L rotated112.5 degrees in a counter-clockwise direction about shoulder axis 16L.Upper arm 14R rotates 206.36 degrees in a counter-clockwise directionalong a circular path segment 358 about shoulder axis 16R in the secondoperational state of controller 54 to keep hand 30R retracted, holdforearm 22R stationary, and position hand 30R in line with processingstation 350.

Frame 10 shows simultaneous rotation of upper arms 14L and 14R. Upperarm 14L rotates 153.65 degrees in a counter-clockwise direction along acircular path segment 360 about shoulder axis 16L in the secondoperational state of controller 54 to keep hand 30L retracted whileholding wafer B, hold forearm 22L stationary, and position hand 30L inline with processing station 350. Upper arm 14R and forearm 22Rcooperatively rotate in the first operational state of motor controller54 to linearly extend hand 30R so as to reach and retrieve wafer A fromprocessing station 350. To accomplish this incremental movement, upperarm 14R rotated 112.5 degrees in a clockwise direction about shoulderaxis 16R.

Frame 11 shows upper arm 14R and forearm 22R cooperatively rotating inthe first operational state of controller 54 to linearly retract hand30R holding wafer A after the application of vacuum pressure at outlet36R to secure wafer A to hand 30R. To accomplish this incrementalmovement, upper arm 14R rotated 112.5 degrees in a counter-clockwisedirection about shoulder axis 16R.

Frame 12 shows upper arm 14L and forearm 22L cooperatively rotating inthe first operational state of motor controller 54 to linearly extendhand 30L so as to reach and place wafer B on processing station 350. Toaccomplish this incremental movement, upper arm 14L rotated 112.5degrees in a clockwise direction about shoulder axis 16L.

Frame 13 shows simultaneous rotation of upper arms 14L and 14R. Upperarm 14L and forearm 22L cooperatively rotate in the first operationalstate of controller 54 to linearly retract hand 30L after the release ofvacuum pressure at outlet 36L to leave wafer B at processing station350. To accomplish this incremental movement, upper arm 14L rotated112.5 degrees in a clockwise direction about shoulder axis 16L. Upperarm 14R rotates 26.35 degrees in a clockwise direction along a circularpath segment 362 about shoulder axis 16R in the second operational stateof controller 54 to keep hand 30R retracted while holding wafer A, holdforearm 22R stationary, and position hand 30R in line with, but facing adirection opposite from, cassette 352R.

Frame 14 shows torso link 11 rotating 180 degrees in a clockwise (orcounter-clockwise) direction about central axis 13 to position hand 30Ladjacent cassette 352R and hand 30R in line with cassette 352L.

Frame 15 shows simultaneous rotation of upper arms 14L and 14R. Upperarm 14R and forearm 22R cooperatively rotate in the first operationalstate of motor controller 54 to linearly extend hand 30R so as to reachand place wafer A in cassette 352L. To accomplish this incrementalmovement, upper arm 14R rotated 112.5 degrees in a clockwise directionabout shoulder axis 16R. Upper arm 14L rotates 26.35 degrees in acounter-clockwise direction along a circular path segment 364 aboutshoulder axis 16L in the second operational state of controller 54 tokeep hand 30L retracted, hold forearm 22L stationary, and position hand30L in line with cassette 352R.

Frame 16 shows simultaneous rotation of upper arms 14L and 14R. Upperarm 14R and forearm 22R cooperatively rotate in the first operationalstate of controller 54 to linearly retract hand 30R after the release ofvacuum pressure at outlet 36R to leave wafer A in cassette 352L. Toaccomplish this incremental movement, upper arm 14R rotated 112.5degrees in a counter-clockwise direction about shoulder axis 16R. Upperarm 14L and forearm 22L cooperatively rotate in the first operationalstate of motor controller 54 to linearly extend hand 30L so as to reachand retrieve wafer C from cassette 352R. To accomplish this incrementalmovement, upper arm 14L rotated 112.5 degrees in a counter-clockwisedirection about shoulder axis 16L.

In this example, upper arm 14L underwent bi-directional rotationalmovement and completed a continuous 378.65 degree cycle in acounter-clockwise direction about shoulder axis 16L before any clockwisecounter-rotation. Torso link 11 underwent rotational movement andcompleted a continuous 180 degree cycle about central axis 13 withoutany counter-rotation. This example demonstrates an ability to make quickexchanges between stations in a layout with a reduced footprint. As anumerical example, because of its ability to collapse its arm links, a21-inch (53 centimeters) diameter robot can manipulate two 12-inch (30.5centimeters) wafers. Robot arm system 8 is also capable of moving hands30L and 30R simultaneously to increase throughput.

FIG. 11 includes 19 frames showing various positions of robot armmechanism 210 of robot arm system 208 in an exemplary operationalsequence that moves a wafer A from wafer cassette 352L to processingstation 350 and to wafer cassette 352R, and moves a wafer B from wafercassette 352L to processing station 350.

In this example, in the initial position shown in frame 1, shoulder axis16 is radially positioned 40.0 centimeters (15.8 inches) from aneffective center 351 of processing station 350 and an effective center353L of cassette 352L. As shown in frame 18, shoulder axis 16 isradially positioned 40.0 centimeters (15.8 inches) from center 351 ofprocessing station 350 and an effective center 353R of cassette 352R.The position of axis 16 in frame 1, the position of axis 16 in frame 18,and centers 353L and 353R define four corners of a rectangle with axes16 (frame 1) and 16 (frame 18) being spaced apart by a distance of 35.5centimeters (14.0 inches) and cassettes 352L and 352R being spaced apartby a distance of 35.5 centimeters (14.0 inches) from center to center.Cassettes 352L and 353R are spaced from respective axes 16 (frame 18)and 16 (frame 1) a non-radial distance of 53.5 centimeters (21.1 inches)measured along the respective diagonals of the rectangle. Torso movementrotation of shoulder 14, as shown in frame 17, radially positions axes16 (frame 1) and 16 (frame 18) a distance of 40.0 centimeters (15.8inches) from respective centers 353R and 353L.

The following description tracks the angular displacement of torso link11 about central axis 13, upper arm 14 about shoulder axis 16, and hands30 ₁ and 30 2 of end effector 230 about wrist axis 32 to demonstrate thecontinuous rotation capabilities of torso link 11 and the mechanicallinks in robot arm mechanism 210.

Frame 1 shows the initial positions of hands 30 ₁ and 30 ₂ retracted andin line with the opening of cassette 352L, with hand 30 ₁ facing in thedirection of and nearer than hand 30 ₂ to cassette 352L. In theseinitial a positions, the central longitudinal axis of upper arm 14(i.e., a line connecting axes 16 and 24) is angularly displaced 90.00degrees in a counter-clockwise direction from a reference line 354.Reference line 354 is perpendicular to a line connecting centers 353Land 353R.

Frame 2 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of motor controller 54 to linearly extend hand30, so as to reach and retrieve wafer A from cassette 352L. Toaccomplish this incremental movement, upper arm 14 rotated 90.00 degreesin a counter-clockwise direction about shoulder axis 16.

Frame 3 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of motor controller 54 to linearly retract hand30 ₁ holding wafer A after the application of vacuum pressure at outlet36 ₁ to secure wafer A to hand 30 ₁. To accomplish this incrementalmovement, upper arm 14 rotated 90.00 degrees, in a counter-clockwisedirection about shoulder axis 16.

Frame 4 shows upper arm 14 rotating 153.65 degrees in acounter-clockwise direction along a circular path segment 366 aboutshoulder axis 16 in the second operational state of motor controller 54to keep hand 301 retracted while holding wafer A, hold forearm 22stationary, and position hand 30, in line with processing station 350.

Frame 5 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly extend hand 30, soas to reach and place wafer A on processing station 350. To accomplishthis incremental movement, upper arm 14 rotated 90.00 degrees in aclockwise direction about shoulder axis 16.

Frame 6 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly retract hand 30,after the release of vacuum pressure at outlet 36, to leave wafer A atprocessing station 350. To accomplish this incremental movement, upperarm 14 rotated 90.00 degrees in a clockwise direction about shoulderaxis 16.

Frame 7 shows upper arm 14 rotating 26.35 degrees in a counter-clockwisedirection along a circular path segment 368 about shoulder axis 16 inthe second operational state of controller 54 to keep hand 30 ₂retracted, hold forearm 22 stationary, and position hand 30 ₂ in linewith cassette 352L.

Frame 8 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly extend hand 30 2 toretrieve wafer B from cassette 352L. To accomplish this incrementalmovement, upper arm 14 rotated 90.00 degrees in a clockwise directionabout shoulder axis 16.

Frame 9 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly retract hand 30 ₂holding wafer B after the application of vacuum pressure at outlet 36 ₂to secure wafer B to hand 30 ₂ To accomplish this incremental movement,upper arm 14 rotated 90.00 degrees in a clockwise direction aboutshoulder axis 16.

Frame 10 shows upper arm 14 rotating 26.35 degrees in a clockwisedirection along a circular path segment 370 about shoulder axis 16 inthe second operational state of controller 54 to keep hand 30 ₂retracted while holding wafer B, hold forearm 22 stationary, andposition hand 30 ₁ in line with and nearer than hand 30 ₂ to processingstation 350.

Frame 11 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly extend hand 30 ₁ soas to reach and retrieve wafer A from processing station 350. Toaccomplish this incremental movement, upper arm 14 rotated 90.00 degreesin a clockwise direction about shoulder axis 16.

Frame 12 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of motor controller 54 to linearly retract hand30 ₁ holding wafer A after the application of vacuum pressure at outlet36 ₁ to secure wafer A to hand 30 ₁. To accomplish this incrementalmovement, upper arm 14 rotated 90.00 degrees in a clockwise directionabout shoulder axis 16.

Frame 13 shows upper arm 14 rotating 180.00 degrees in a clockwise (orcounter-clockwise) direction along a circular path segment 372 aboutshoulder axis 16 in the second operational state of motor controller 54to keep hand 30 ₁ retracted while holding wafer A, hold forearm 22stationary, and position hand 30 ₂ in line with processing station 350.

Frame 14 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly extend hand 30 ₂ soas to reach and place wafer B on processing station 350. To accomplishthis incremental movement, upper arm 14 rotated 90.00 degrees in aclockwise direction about shoulder axis 16.

Frame 15 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of controller 54 to linearly retract hand 30 ₂after the release of vacuum pressure at outlet 36 ₂ to leave wafer B atprocessing station 350. To accomplish this incremental movement, upperarm 14 rotated 90.00 degrees in a clockwise direction about shoulderaxis 16. Upon completion of the incremental movements shown in frames8-15, upper arm 14 underwent a continuous 746.35 degree cycle ofclockwise rotation without any counter-rotation.

Frame 16 shows upper arm 14 rotating 45.00 degrees in acounter-clockwise direction along a circular path 374 about shoulderaxis 16 in the second operational state of controller 54 to keep hand 30₁ retracted while holding wafer A and hold forearm 22 stationary.

Frame 17 shows torso link 11 rotating 180 degrees in a clockwise (orcounter-clockwise) direction about central axis 13 to position hand 30 ₂adjacent cassette 352R and hand 30 ₁ adjacent, but facing a directionopposite from, cassette 352R.

Frame 18 shows upper arm 14 rotating 161.35 degrees in acounter-clockwise direction along a circular path 376 about shoulderaxis 16 in the second operational state of controller 54 to keep hand 30₁ retracted, hold forearm 22 stationary, and position hand 30 ₁ in linewith cassette 352R.

Frame 19 shows upper arm 14 and forearm 22 cooperatively rotating in thefirst operational state of motor controller 54 to linearly extend hand30 ₁ so as to reach and place wafer A in cassette 352R. To accomplishthis incremental movement, upper arm 14 rotated 90.00 degrees in aclockwise direction about shoulder axis 16.

In this example, upper arm 14 underwent bi-directional rotationalmovement and completed a continuous 746.35 degree cycle in a clockwisedirection about shoulder axis 16 without any counter-clockwise rotation.Torso link 11 underwent rotational movement and completed a continuous180 degree cycle about central axis 11 without any counter-rotation.

Robot arm systems 8 and 208 provide different benefits, depending on theapplication. Robot arm 208 is more cost effective because it requiresfewer parts to rotate the robot arm links around four axes, as comparedwith the six axes of robot arm system 8. Robot arm system 208 is fasterand more compact for transporting large specimens because robot armmechanism 210 requires less working space to sweep the specimen aboutthe central axis. As a consequence, robot arm system 208 is moreamenable to complex path planning. On the other hand, robot arm system 8is easier to “teach” to perform the necessary hand movement toaccomplish the exchange functions desired.

Robot arm systems 8 and 208 provide extended reach in that all links canbe serially extended. To match the same length of extension, aconventional three-link robot arm mechanism would require a much greaterfootprint because of a limited ability to collapse its length. Moreover,there are geometrical limits to a reacharound capability withconventional three-link robot arm mechanisms, which perform linear movesby following a path defined by the radial line connecting the shoulderaxis to the end of the hand. The present invention described above iscapable of performing linear moves without following a radial path.

The above example presented with reference to FIGS. 6A and 6B showsside-by-side coplanar or parallel arrangement of the openings of waferholders or carriers 168 _(l) and 168 _(r) and, therefore, represents aretrieval of wafers stored in carriers not positioned a radial distancefrom shoulder axis 16R. In a front-opening unified pod (FOUP)-basedsystem, wafer carriers positioned side by side are often misaligned fromtheir nominal coplanar opening arrangement relative to the robot armmechanism. This condition typically results from misalignment of supportstructures on which support structure mounting elements such askinematic coupling pin mountings are placed to receive the mountingfeatures positioned on the bottom surfaces of the wafer carriers. Suchmisalignment could cause a robot arm mechanism to direct the hand or thewafer it carries to strike the wafer carrier instead of extend into itsopening to, respectively, remove or replace a wafer. Misalignment cantherefore result in contaminant particle creation stemming from impactof the hand or wafer against the wafer carrier.

The mathematical expressions derived with reference to FIG. 6A for thepath of travel of hand 30, together with the angular positions of motors50R and 52R tracked by the respective glass scale encoders 106R and108R, provide position output information of robot arm mechanism 10Rthat can be used to compensate for this misalignment. (This assumes thatthe angular position of motor 92, which is tracked by glass scaleencoder 118, remains fixed during movement of robot arm mechanism 10R.)

The position output information can be used to provide offset data foreither mechanical alignment of the system components such as, forexample, wafer carriers, or control the trajectory of robot armmechanism 10R to compensate for support structure alignment offset. Amisalignment correction technique carried out in accordance with thepresent invention entails the use of a component emulating fixturehaving mounting features that are matable to the support structuremounting elements. The emulating fixture preferably includes twoupwardly extending, cylindrical locating features that are positioned toengage a fork-shaped end effector in two different extension positions.For manual correction, robot arm mechanism position output informationprovides the angular offset between the actual and nominal radialdistances between the shoulder axis and the two locating features, oneof which positioned at the effective center of a wafer properly storedin the wafer carrier. Position coordinates for proper alignment bymanual repositioning is of any misaligned wafer carrier can then bederived. For automatic correction, robot arm mechanism position outputinformation is used to derive a vector trajectory that causes the endeffector to properly access the wafers stored in a misaligned wafercarrier.

FIGS. 12-19, together with their associated descriptions, present aself-teaching method with reference to a three-link robot arm mechanism10 for a preferred use with FOUP-based system wafer carriers. Robot armmechanism 10 is of the same design as that of each of robot armmechanisms 10L and 10R.

FIG. 12 shows an upper surface 400 of a support structure 402 adapted toreceive a front-opening wafer carrier 404 (FIG. 13A) for 300 mm diametersemiconductor wafers. Three kinematic coupling pins 406 are positionedon upper surface 400 in locations required under SEMI E47.1 (Mar. 5,1998). A pivotable latch 408 includes a clamping finger 410 configuredto mate with a carrier front retaining or clamping feature 412 (FIGS.13B and 13C).

FIG. 13A shows wafer carrier 404 with its door (not shown) removed toreveal in the interior of wafer carrier 404 a wafer cassette 414 withits slots 416 spaced apart to accommodate stacked 300 mm diametersemiconductor wafers. FIGS. 13B and 13C show, respectively, a bottomsurface 430 and carrier front retaining feature 412 on bottom surface430 of wafer carrier 404. A preferred wafer carrier 404 is a model F300wafer carrier manufactured by Fluoroware, Inc., Chaska, Minn.

With reference to FIG. 13B, wafer carrier 404 has on its bottom surface430 five carrier sensing pads 432, two advancing carrier sensing pads434, a carrier capacity (number of wafers) sensing pad 436, a carrierinformation pad 438, and one each of front end of line (FEOL) and backend of line (BEOL) information pads 440 required under SEMI E47.1 (Mar.5, 1998). Three oblong, inwardly sloped depressions in bottom surface430 form kinematic pin receiving features 444 that mate with kinematiccoupling pins 406 (FIG. 12) fixed in corresponding locations on supportstructure 402 when wafer carrier 404 is properly installed. Withreference to FIGS. 13B and 13C, a depression 446 partly covered by aprojection 448 having a beveled surface 450 forms front retaining andclamping feature 412. Beveled surface 450 provides a ramp along which awheel or roller can roll up to clamp against projection 448.

FIGS. 14A and 14B are respective bottom and top plan views of acomponent emulating fixture 460. With reference to FIG. 14A, fixture 460is dimensioned to define a footprint that allows it to fit in the spaceoccupied by wafer carrier 404 and includes in its bottom surface 462three oblong, inwardly sloped depressions 464 and a carrier frontretaining feature 466, all of which are of the same types and arepositioned in the same corresponding locations as kinematic pinreceiving features 444 and retaining feature 412 in bottom surface 430of wafer carrier 404.

With reference to FIG. 14B, fixture 460 has extending upwardly from itsupper surface 470 first and second locating features 472 and 474 ofpreferably cylindrical shape with different heights. Locating feature472 is positioned so that its longitudinal axis 476 is preferably set atthe location of the effective center 478 of a wafer 480 stored in wafercassette 414, and locating feature 474 is positioned so that itslongitudinal axis 482 is preferably set forward of the location of theopen front of wafer carrier 404. Locating feature 472 is taller thanlocating feature 474, and the free ends of locating features 472 and 474terminate in respective top caps 484 and 486. The functions of locatingfeatures 472 and 474 are described below. Fixture 460 fits in the workspace dedicated for occupancy by wafer carrier 404 and is matable,therefore, to the mounting elements, including kinematic coupling pins406 and clamping feature 412, provided in upper surface 400 of supportstructure 402.

FIGS. 15A and 15B are respective diagrammatic cross-sectional and rearend elevation views of fixture 460. FIG. 15A shows the detail of theshape of and features provided in bottom surface 462 of fixture 460, andFIG. 15B shows the fit of a kinematic coupling 406 within the depression464 located nearest the rear of bottom surface 462 of fixture 460. FIGS.15A and 15B show that the height of locating feature 474, defined withreference to the top surface of top cap 486, is set to the position ofthe bottom wafer stored in wafer cassette 414. Locating feature 472 istaller than locating feature 474 to provide for robot arm mechanism 10access to the more distant locating feature 472.

FIGS. 16A, 16B, and 16C are, respectively, a bottom plan view of fixture460 superimposed on an outline of wafer carrier 404, a side elevationview of fixture 460 similar to that of FIG. 15A of fixture 460, and rearend view of fixture 460 inverted relative to that of FIG. 15B of fixture460. FIG. 16A shows the coincidence of the placement of effective center478 of a wafer 480 and longitudinal axis 476 of locating feature 472, aswell as the coincidence of the two respective kinematic pin receivingfeatures 444 of wafer carrier 404 and depressions 464 of fixture 460.

FIG. 17 shows wafer carriers 404 _(l) and 404 _(r) positioned side byside with their front openings in coplanar relation, similar to thatdepicted in FIG. 6A. FIG. 18 shows wafer carriers 404 _(l) and 404 _(r)positioned side by side but with wafer carrier 404 _(l) offset such thatthe front openings of wafer carriers 404 _(l) and 404 _(r) aremisaligned from the nominal coplanar position shown in FIG. 17.

With reference to FIGS. 17 and 18, three link robot arm mechanism 10 ispositioned to extend its end effector 30 to reach each of first andsecond locating features 472 and 474 of fixtures 460 _(l) and 460 _(r)to acquire for each of them two sets of extension position data formeasuring the actual positions of wafer carriers 404 _(l) and 404 _(r)and thereby the relative alignment between them. Direction arrows 500show the straight line move required to withdraw wafer 480 from eitherof wafer carriers 404, and 404 _(r). Wafer 480 is shown in two positionsalong the straight line trajectory with effective center 478 of wafer480 coincident with respective longitudinal axes 476 and 482 of locatingfeatures 472 and 474. Skilled persons will appreciate that locatingfeature's 472 and 474 need not lie along a straight line path of robotarm movement but only reside in known locations. There is no restrictionof the number of locating feature points, so long as their locations areknown.

Robot arm mechanism 10 is positioned away from and between the positionsof the front openings of wafer carriers 404 _(l) and 404 _(r) but not ata location equidistant between the effective centers 478 of the wafers480 stored in them. A broken line circle 502 represents the perimeter ofthe distal end of end effector 30 when it is fully extended andangularly displaced 360 degrees about its shoulder axis 16. Circle 502does not, therefore, intersect the effective centers 478 of wafers 480stored in cassettes 414 _(l) and 414 _(r) of FIG. 17.

The position coordinates of the desired orientations of wafer carriers404 _(l) and 404 _(r) derived from the two sets of robot arm positiondata acquired by causing robot arm end effector 30 to contact each oflocating features 472 and 474. In a preferred manner of operation, auser manually places end effector 30 against each locating feature 472and 474, and the available robot arm mechanism data are acquired asdescribed with reference to FIGS. 6A and 6B. The actual positioncoordinates of locating features 472 and 474 are compared against thenominal position coordinates of wafer carrier 404 _(l) to compute anyoffset or deviation from a nominal alignment relative to shoulder axis16 of robot arm mechanism 10. Equipping robot arm mechanism 10 withZ-axis displacement control and measurement along the length of shoulderaxis 16 would provide an ability to place end effector 30 against lowersurfaces 488 and 490 of the respective top caps 484 and 486 and measurethe heights of locating fixtures 472 and 474. This would provideposition coordinates for two points not at the same elevation inthree-dimensional space, from which a skilled person can deriveinformation for each of six degrees of freedom.

FIG. 19 is a diagram showing radii R₀ and R₁ representing distancesbetween shoulder axis 16 and longitudinal axes 476 and 482 for,respectively, the extension of end effector 30 to locating features 472₁ and 474 ₁ for wafer carrier 404 ₁. The following mathematicalexpressions demonstrate the derivation from known robot arm mechanismparameters the required position coordinates for wafer carrier 404 ₁ toeffect a straight line move for withdrawing wafer 480 as depicted inFIGS. 17 and 18. With reference to FIG. 19, the positions of locatingfeatures 472 ₁ and 474 ₁ are represented by position coordinates (X, Y₀)and (X, Y₁), respectively, and shoulder axis 16 as represented byposition coordinates (0, 0). The robot arm extensions R₀ and R₁ areexpressed as follows:

R₀ ²=X²+Y₀ ²=X²+(Y₁+D)²=X²+Y₁ ²+2Y₁D+D²  (4)

R₁ ²=X²+Y₁ ², where   (5)

D is the distance between longitudinal axes 476 ₁ and 482 ₁ (i.e.,(Y₀−Y₁)). Subtracting R₁ ² from R₀ ² gives

R₀ ²−R₁ ²=2Y₁D+D².  (6)

Solving equation (6) for Y₁ and squaring the result gives$\begin{matrix}{Y_{1}^{2} = {\frac{1}{4D^{2}}{\left( {R_{0}^{2} - R_{1}^{2} - D^{2}} \right)^{2}.}}} & (7)\end{matrix}$

Solving equation (5) for X² gives

X²=R₁ ²−Y₁ ²,  (8)

and substituting the right-hand side of equation (7) for Y₁ ² gives$\begin{matrix}{X^{2} = {R_{1}^{2} - {\frac{1}{4D^{2}}{\left( {R_{0}^{2} - R_{1}^{2} - D^{2}} \right).}}}} & (9)\end{matrix}$

Applying the law of cosines to solve for D as a function of α, which isthe included angle between R₀ and R₁, gives

D²=R₀ ²+R₁ ²−2R₀R₁ cos α  (10)

Equations (7) and (9) can be solved from the robot arm mechanismparameters θ_(REF0), the angle of motor 52 when end effector 30 contactslocating feature 472 ₁, and θ_(REF1), the angle of motor 52 when endeffector 30 contacts locating feature 474 ₁. The angles θ_(REF0) andθ_(REF1) equal arcsin X/R₀ and arcsin X/R₁, respectively; and the angleα=θ_(REF0)−θREF₁.

The foregoing expressions dictate what the position coordinates shouldbe for a properly aligned system. The motor angles available from glassscale encoders can give the appropriate information for controller 54 tooffset the necessary parameters to give the motion of robot armmechanism or provide a read out to the operator indicative of how toreposition wafer carrier 404 _(l) to get the desired positioncoordinates. The “automatic training” of the robot arm mechanism pathoption is greatly preferred because it affords a software adjustmentsolution as an alternative to a difficult, time-consuming mechanicalalignment solution. The mechanical alignment solution is necessary forrobot arm mechanisms that are incapable of moving wafers or otherspecimens along nonradial paths.

Skilled persons will appreciate that the equations of motion set forthabove pertain to a three link robot arm mechanism with a one-to-one linkratio. The present invention can, therefore, be implemented with robotarm mechanisms having different numbers of links and/or different linkratios. For example, the invention can be implemented with a telescopicrobot arm mechanism.

It will be obvious to those having skill in the art that many changesmay be made to the details of the above-described embodiments of thisinvention without departing from the underlying principles thereof. As afirst example, the invention can be used with a different specimenholder such as a wafer prealigner, on top of which a wafer is placed. Asa second example, proper registration of the component emulating fixtureneed not be achieved by mounting features matable to support structuremounting elements but could be accomplished by other techniques, such asoptical (e.g., a video camera) or quadrature signal alignment detectiontechniques. The scope of the present invention should, therefore, bedetermined only by the following claims.

What is claimed is:
 1. In a specimen processing system that includes arobot arm mechanism in nominal alignment relative to a specimen holderpositioned on a support surface of a support structure and having aclear area through which an end effector reaches to remove a specimenfrom or place a specimen in or on the specimen holder, the supportsurface of the support structure having mounting elements and thespecimen holder having alignment surface features that are matable tothe mounting elements, a method of determining an actual alignment ofthe robot arm mechanism relative to the specimen holder that differsfrom the nominal alignment to ensure that the end effector can removespecimens from and place specimens in the holder, comprising: placing acomponent emulating fixture on the support surface of the supportstructure, the fixture being matable to the mounting elements to assurethe actual alignment position of the specimen holder and including firstand second locating features positioned to engage the end effector intoextension position; positioning the robot arm mechanism to contact thefirst locating feature to acquire a first set of robot arm positiondata; positioning the robot aim mechanism to contact the second locatingfeature to acquire a second set of robot arm mechanism position data;and using the first and second sets of robot arm mechanism position datain conjunction with robot arm mechanism equation of motion to determinewhether alignment positioning of the specimen holder relative to therobot arm mechanism represents an offset in the actual alignment inrelation to the nominal alignment.
 2. The method of claim 1, furthercomprising providing the first and second position coordinateinformation in a form usable for manual relative repositioning of thespecimen holder and the robot arm mechanism to correct for the alignmentoffset.
 3. The method of claim 1, further comprising reprogramming therobot arm mechanism to control its trajectory to eliminate positionerror caused by the alignment offset.
 4. The method of claim 1 in whichthe first and second locating features extend upwardly of the fixtureand are of different heights so as to allow the robot arm mechanism toaccess and engage both of them.
 5. The method of claim 1 in which thefirst and second locating features are offset along different radialpaths so as to allow a robot arm mechanism to access and engage both ofthem.
 6. The method of claim 1 in which one of the first and secondlocating features is located at the true center of a wafer stored in thespecimen holder when positioned correctly on the support structure. 7.The method of claim 1 in which the locating features are of cylindricalshape and the end effector has a distal fork-shaped end that engageseach of the locating features in a manner that self centers on thelocating feature.
 8. In a specimen processing system that includes arobot arm mechanism in nominal alignment relative to a specimen holderpositioned on a support surface of a support structure and having aclear area through which an end effector reaches to remove a specimenfrom or place a specimen in or on the specimen holder, a method ofdetermining an actual alignment of the robot arm mechanism relative tothe specimen bolder that differs from the nominal alignment to ensurethat the end effector can remove specimens from and place specimens inthe holder, comprising: placing a component emulating fixture on thesupport surface of the support structure, the fixture being adapted toassume the actual alignment position of the specimen holder andincluding first and second locating features positioned to engage theend effector into extension position; positioning the robot armmechanism to contact the first locating feature to acquire a first setof robot arm position data; positioning the robot arm mechanism tocontact the second locating feature to acquire a second set of robot armmechanism position data; and using the first and second sets of robotarm mechanism position data in conjunction with robot arm mechanismequations of motion to determine whether alignment positioning of thespecimen holder relative to the robot arm mechanism represents an offsetin the actual alignment in relation to the nominal alignment.
 9. Themethod of claim 8, further comprising providing the first and secondposition coordinate information in a form usable for manual relativerepositioning of the specimen holder and the robot arm mechanism tocorrect for the alignment offset.
 10. The method of claim 8, furthercomprising reprogramming the robot arm mechanism to control itstrajectory to eliminate position error caused by the alignment offset.11. The method of claim 8 in which the first and second locatingfeatures extend upwardly of the fixture and are of different heights soas to allow the robot arm mechanism to access and engage both of them.12. The method of claim 8 in which the fixture is adapted to assume theactual position of the specimen holder by an indirect alignmenttechnique.
 13. The method of claim 12 in which the indirect alignmenttechnique entails the use of a video camera.